Photographic processes using silver halide have been most widely used in the past due to their excellent photographic properties such as sensitivity or control of gradation, etc., as compared with other photographic processes, such as an electrophotographic process or a diazo photographic process. In recent years, with respect to image formation processes for light-sensitive materials using silver halide, many techniques capable of easily and quickly obtaining images have been developed by changing the conventional wet process using a developing solution into a dry development process such as a process using heat, etc.
Heat-developable light-sensitive materials are known in the field of these techniques. Heat-developable light-sensitive materials and processes therefor have been described, for example, in Shashin Kogaku no Kiso (The Foundation of Photographic Technology), pages 553 to 555 (published by Corona Co., 1979), Eizo Jyoho (The Image Information), page 40 (April, 1978), Nebletts Handbook of Photography and Reprograph, 7th Ed., pages 32 to 33 (Van Nostrand Reinhold Company), U.S. Pat. Nos. 3,152,904, 3,301,678, 3,392,020 and 3,457,075, British Pat. Nos. 1,131,108, and 1,167,777, and Research Disclosure, No. 17029, pages 9 to 15 (June, 1978).
Many different processes for obtaining color images have been proposed. With respect to processes for forming color images by the reaction of an oxidation product of a developing agent with a coupler, it has been proposed to use a p-phenylenediamine type reducing agent and a phenolic coupler or an active methylene coupler as described in U.S. Pat. No. 3,531,286, a p-aminophenol type reducing agent as described in U.S. Pat. No. 3,761,270, a sulfonaimidophenol type reducing agent as described in Belgian Pat. No. 802,519 and Research Disclosure, pages 31 and 32 (Sept., 1975) and the combination of a sulfonamidophenol type reducing agent and a 4-equivalent coupler as described in U.S. Pat. No. 4,021,240. These processes, however, are disadvantageous in that turbid color images are formed, because a reduced silver image and a color image are silultaneously formed on the exposed area after heat-development. In order to eliminate these disadvantages, there have been proposed a process which comprises removing a silver image by liquid processing or a process which comprises transferring only the dye to another layer, for example, a sheet having an image receiving layer. However, the latter process is not desirable because it is not easy to transfer only the dye as distinguishable from unreacted substances.
Another process which comprises introducing a nitrogen containing heterocyclic group into a dye, forming a silver salt and releasing a dye by heat-development has been described in Research Disclosure, No. 16966, pages 54 to 58 (May, 1978). According to this process, clear images cannot be obtained, because it is difficult to control the release of dyes from nonexposed areas, and thus it is not a conventionally applicable process.
Also, processes for forming a positive color image by a light-sensitive silver dye bleach process, with useful dyes and methods for bleaching have been described, for example, in Research Disclosure, No. 14433, pages 30 to 32 (April, 1976), ibid., No. 15227, pages 14 and 15 (Dec., 1976) and U.S. Pat. No. 4,235,957.
However, this process requires an additional step and an additional material for accelerating bleaching of dyes, for example, heating with a superposed sheet with an activating agent. Furthermore, it is not desirable because the resulting color images are gradually reduced and bleached by coexisting free silver during long periods of preservation.
Moreover, a process for forming a color image utilizing a leuco dye has been described, for example, in U.S. Pat. Nos. 3,985,565 and 4,022,617. However, this process is not desirable because it is difficult to stably incorporate the leuco dye in the photographic material and coloration gradually occurs during preservation.
Moreover, these methods described above have disadvantages in that a relatively long time is generally required for development and that only images having a high level of fog and a low density are obtained.
In order to eliminate these drawbacks, a method of forming an image has been proposed in which a mobile dye is is imagewise formed utilizing silver halide and the dye is transferred to a dye fixing layer (as described in European Patent Application (OPI) No. 76492). According to the method a light-sensitive material containing silver halide and a dye releasing redox compound which functions to the silver halide as a reducing agent at an elevated temperature and at the same time is oxidized to release a mobile dye is heated under the condition substantially free from water after or simultaneously with exposure to form imagewise a mobile dye and transferring the mobile dye to a dye fixing layer.
In such a image forming method, both a step for forming edgewise mobile dyes by heating and a step for transferring the dyes to a dye fixing layer are indispensable. If these two steps can be carried out at the same time, a more rapid and easy processing is possible. As a result of various investigations from this point of view, it has been found that it is possible by heating at a temperature lower than a boiling point of a solution a light-sensitive material superposed on a dye fixing material under the condition maintaining water in the presence of a base or a base precursor capable of releasing a base by heating. It has also been found that in the so-called mono-sheet type light-sensitive material in which a dye fixing layer is incorporated into a light-sensitive material it is possible when the material is heated under the condition maintaining water by means of close contact with a material hardly permeating moisture such as a polyethylene terephthalate film, etc.